CNN  — 

Ashton Kutcher revealed Monday he had battled a serious autoimmune disease that affected his hearing, sight and ability to walk for more than a year.

“Like two years ago, I had this weird, super-rare form of vasculitis,” Kutcher said in an exclusive video clip released to “Access Hollywood” from an upcoming episode of National Geographic’s “Running Wild with Bear Grylls: The Challenge.”

“Knocked out my vision, knocked out my hearing, knocked out like all my equilibrium. It took me like a year to like build it all back up,” Kutcher told adventurer and presenter Bear Grylls as they hiked through brambles and trees.

“You don’t really appreciate it until it’s gone, until you go, ‘I don’t know if I’m ever gonna be able to see again. I don’t know if I’m gonna be able to hear again, I don’t know if I’m going to be able to walk again,” Kutcher said. “I’m lucky to be alive.”

CNN has reached out to Kutcher’s representative but has not yet received a response.